1. Field of the Invention
The present invention is directed to an iron effect pigment.
2. Background Art
Flakes of iron are produced according to the current standard technology from granular iron, which is obtained by atomizing molten iron. The pigment production takes place by means of crushing or milling processes whereby the granules are reduced to small pieces and deformed. As with all metal pigment production methods, lubricants are added in the process to prevent cold welding of the pigment particles. The standard technology for producing flake shaped iron pigment is described in detail in examples 1 and 8 in EP 0673 980. The shortcomings of that production process lie in the fact that granular iron that is produced by atomizing is always relatively coarse and has a wide particle size distribution. As a result, only relatively large flakes can be produced from granular iron produced by atomizing. Flakes in the preferred range for effect pigments of 6 to 36 xcexcm can be obtained only through energy extensive and lengthy grinding processes, or one has to limit oneself to using sieve fractions before and/or after the grinding. This makes their production unprofitable. The shape of the iron flakes that are obtained by atomizing is irregular, with rough surfaces and frayed edges, which results in a relatively low optical quality due to a greater number of light-scattering centers.
Metal flakes of high optical quality can be obtained by grinding only if the grinding process is performed so gently that the granules are merely deformed and not reduced in size. The prerequisite for such a gentle grinding is a high ductility of the metal granules, which is present in aluminum, for example. As is well known, aluminum flakes of a particularly high optical quality can be produced by using granules of spherical morphology. If these granules are merely deformed and not reduced in size during the grinding, flakes are obtained that have round edges and a smooth surface (so-called xe2x80x9csilver dollarsxe2x80x9d). Because of their regular shape, due to the lesser light scattering when applied in a coating, these pigments have a significantly more directed reflection of incoming light than pigments of a comparable size distribution that, however, were obtained from shapeless granules and/or by reduction in size.
Optically even superior metal pigments can be produced by physical vapor deposition (PVD) processes. In this alternate technology, metal films are deposited onto substrates in the vacuum and subsequently removed and pulverized. Those pigments, however, are disproportionately expensive and, with the exception of aluminum, have so far found no application. Iron flakes that could possibly be produced according to that method have been left out of account within the framework of this invention.
Flakes from iron alloys, such as alloyed special steelxe2x80x94or Hastalloyxe2x80x94flakes are also not an object of the present invention. They generally lack the specific shade and luster of iron. Furthermore, iron alloys usually display a less favorable ductility and a lesser or no utilizable magnetism.